The poinsettia (Euphorbia pulcherrima) is a tropical shrub known for its vibrant colors, making it a symbol of winter holidays. The colorful parts are not flowers but modified leaves called bracts. Under typical indoor conditions, the color generally lasts between four and eight weeks from the time of purchase. With careful attention to its environmental needs, it is possible to maintain the colored bracts until early spring, potentially extending the display for several months.
The Biology of Color: Bracts and Photoperiodism
The distinctive red, pink, or white hues of the poinsettia come from its bracts, which are specialized leaves that gather around the plant’s true, inconspicuous flowers. These small, yellow structures at the center of the bract cluster are called cyathia. The coloration of the bracts is a physiological response designed to attract pollinators.
This color change is governed by photoperiodism, classifying the poinsettia as a “short-day” plant. The plant requires a sustained period of long, uninterrupted darkness each night to trigger the production of vibrant pigments. The red color is due to the accumulation of anthocyanins, which are water-soluble pigments synthesized within the plant’s cells.
The plant perceives the length of the dark period, not the length of the day, as its signal to transition to coloring. If the necessary dark period is interrupted by even a brief flash of light, the process can be stalled or reversed. This sensitivity explains why the bract color will eventually begin to fade once the plant is exposed to the longer days and artificial light of a typical home environment.
Extending the Display: Care Factors for Longevity
To maximize the duration of the poinsettia’s existing color, the focus must be on maintaining a stable, tropical-like environment. The plant requires bright, indirect light for at least six hours daily to support photosynthesis and pigment retention. Placing it near an east-facing or south-facing window that is shielded from harsh direct sun is generally ideal.
Watering is the most frequent cause of premature decline, as the plant reacts poorly to both waterlogged soil and complete dryness. Only water the plant when the soil surface feels dry to the touch, checking the top inch of the potting mix. When watering, apply enough liquid so that it drains fully out of the bottom of the pot. Immediately empty any standing water from the saucer or decorative foil wrapping to prevent root rot.
The poinsettia is highly sensitive to temperature fluctuations and drafts, which can cause the colored bracts and green leaves to drop prematurely. The plant thrives in a comfortable room temperature, ideally between 60°F and 70°F during the day. Nighttime temperatures should not drop below 55°F. The plant must be kept away from cold windowpanes, exterior doors, and heating or cooling vents.
Maintaining stable humidity helps prevent the bract edges from browning and curling. Since most homes are dry during the winter, placing the pot on a saucer filled with pebbles and water will create a localized humid microclimate around the plant. Avoid applying fertilizer while the plant is in full color, as this can stimulate new green growth at the expense of the colored display.
The Multi-Step Process for Next Season’s Color
If you wish to encourage your poinsettia to develop new colored bracts for the following holiday season, a complex, year-long schedule must be followed.
Spring and Summer Growth
Once the current bracts begin to fade, typically in late winter or early spring, the plant should be pruned back to a height of about four to six inches. This post-holiday pruning forces the plant into a period of semi-dormancy, after which new growth will emerge. Throughout the spring and summer, the plant should be treated as a standard houseplant, receiving bright light and consistent watering as it enters an active growth phase.
Once the danger of frost has passed and outdoor nighttime temperatures remain above 50°F, the poinsettia can be moved outside. Place it in a spot with morning sun and afternoon shade. During this time of active growth, apply a balanced houseplant fertilizer every two to four weeks.
Fall Re-Coloration
The critical step for re-coloration begins in the fall, around October 1st, when the plant must be subjected to a strict light-control regimen for eight to ten weeks. This involves providing 14 hours of total, uninterrupted darkness every single night. The plant can be placed in a dark closet or covered with an opaque box from 5 p.m. until 7 a.m. the following morning.
During the remaining daylight hours, the plant must be returned to a location where it receives bright light to support photosynthesis. Even a momentary interruption of the dark period, such as light filtering through a crack in a closet door, can reset the photoperiodic cycle and prevent the bracts from coloring. Once the bracts show significant color, the darkness treatment can be stopped, and the plant is ready for display.